Iron casting



Patented June 15, 1926 UNITED STATES PATENT OFFICE.

JOSEPH ERNST FLETCHER, OF DUDLEY, AND HORACE JOHN YOUNG, 01E WHITLEYBAY, NORTHUMBERLAND, ENGLAND.

IRON CASTING.

No Drawing. Application filed March 18 1926, Serial No. 95,764, and inGreat Britain October 1, 1924.

This invention relates to iron castings to form machine and engineparts, and for other purposes, and has for its object the production ofsaid castings insuch manner as will ensure h'omogeneity, toughness,close grain, and resistaiice to wear attrition, abrasion or erosion,together with high tensile strength and capacity to withstand shocks orsuddenly applied loads at normal or el evated temperatures andpressures.

The invention comprises the manufacture of iron castings in the mannerhereinafter described.

The iron We employ in our castings contains preferably lessthan 3.5 percent of carbon, but the other elements may be in the proportionscommonly found in commercial cast irons though preferably in lessproportions than those associated with the production of soft or easilymachinable castmgs.

The internal structure or physical condition ofv the iron we propose toemploy in our castings before treatment is that known as hypoeutectic,the mass of its ferrous grains being more or less embedded in a meshworkconsisting mainly of iron and other carbides and phosphides, whilstgraphitic carbon is present as flakes or nodules of preferably smalldimensions.

In the making of our castings these are cast and cooled, either inmoulds of sand, plaster, plumbago, graphite of other like reractory theuse of chills and in ot ers the use of warm or hot moulds, or in mouldssuch as those made of iron, steel or other metals which are usuallypreheated. The composition of the cast iron is regulated and additionsof other metals or metalloids may be made, in order to favour .theproduction of metal'in which the pearlitic condition predominates.

Further, the castin s are, if necessary reheated in order to o tain orcomplete the predominantly pearlitic condition. The re heating may beeffected by immersion of the castings in molten metal or molten salts.

The pearlitic or predominantly pearlitic casting so obtained is nextreheated either byordinary means or by immersion in molten metal ormolten salts, to a temperature above the critical temperature associatedwith the formation of pearlite and known as A0,, and'then quickly cooledwith air, oil,

materials includin in some cases water, steam or as molten metal othercoolin medium, such or molten sa ts, whereby the structure of the metalis converted to that known as. austenitic or partly austeniticacondition inwhich the carbon or carbides are considered to be dissolvedmore or less homogeneously temperature or cooling is said tion.

The casting in the iron which, at the temperature range used for to bein the gamma condiin the said austenitic condition is then reheated to atemperature not exceeding" and preferably below the aforesaid criticalchange point denoted Ac, and

quickly cooled.

The reheating may be eliected in either of the following ways (1) Themolten metal or salts together With' the castin g immersed therein arereheated to a temperature not exceeding and preferably belo w the saidcritical change point A0,. The casting is then withdrawn from the moltenmetal or salts and cooled.

(2) The casting alone, after withdrawal from the molten metal or saltsis reheated to the extent aforesaid and cooled. Such reheating andrecoolings may be accomplished by immersion in other baths of moltenmetal or salts of suitable temperature, or by other Such treatmentproduces a fication of the further modi- '85 metal structure in that theferrous grains take up the conditions known in ferrous metallography assorbitic, troostitic, or marten acteristics of toughness "and effectiveresistance to shocks.

treatments for austenitic or partly austenitic and, second,

of the sorbitic combined in another way thus :The castor other structuremay be ing in the predominantly pearlitic condition first producedduring the primary casting or by means of a further reheating asaforedescribed is reheated to above the critical point Ac,, but

cooled down quenched briskl 'removed there cient heat to br instead ofbeing completely 0 from such temperature it is in the cooling medium androm whilst retaining sufliing about the desired structure aforesaidwithout the necessity for the 9 third operation fore described.

or treatment as hereinbe It is known that the said structures areoccasionally unintentionally,

produced partially in cast iron,

but the sorbite, martensite and troostite present are heterogeneouslymixed with other constituents which destroy the tough condition soughtfor. By our invention we produce a predominantly sorbitic, troostitic ormartensitic or combined structure of uniform character throughout themass of the ferrous grains of the castings formed as aforesaid fromirons of preferably hypoeutectic composition.

To facilitate the formation of the desired structure there may be usedin the mixtures from which the castings are made additions of such othermetals or metalloids as will, without preventing the formation of thepearlitic structure by the primary treatment or treatments, promote theformation of the austenitic and sorbitic or troostitic conditions orstructures by the second or third treatments or operations.

Thus, for example, nickel, cobalt, molybdenum, tungsten, Vanadium,boron, or chromium may be used for such purpose.

Having thus described our invention what we claim as new and desire tosecure by Letters Patent is l. A process for the production of cast ironcastings which comprises forming a casting with a predominatelypearlitic structure, transforming said pear-litic structure intoaustenitic structure and said stable austenitic structure to a formintermediate pearlite and austenite.

2. A process for the production of cast iron casting which comprisesforming a casting with a predominately pearlitic structure, heating saidcasting to above the Ac, point, cooling said casting so as to formstable austentic structure, reheating said casting to the Ac point as amaximum and cooling said casting so as to decompose said austenticstructure to a form intermediate pearlite and austenite.

In testimony whereof we have signed our names to this specification.

JOSEPH ERNST FLETCHER. HORACE JUHN YOUNG.

decomposing

